Microinjection molding (µIM) is considered to be one of the most flexible, reliable and cost effective manufacturing routes to form plastic micro-components for microsystems. The molding machine, mold tool fabrication, material selection and process controlling in this specific field have been greatly developed over the past decades. This review aims to present the new trends towards improving micro-component performance by reviewing the latest developments in this area and by considering potential directions. The key concerns in product and mold designing, essential factors in simulation, and micro-morphology and resultant properties are evaluated and discussed. In addition, the applications, variant processes and outlook for µIM are presented. Throughout this review, decisive considerations in seeking improved performance for microsystem components are highlighted.

https://iopscience.iop.org/article/10.1088/0960-1317/23/9/093001/pdf

Microinjection molding of microsystem components: new aspects in improving performance

Injection molding is the most widely used processing technique for polymers. It offers several advantages over other processing conditions such as good surface finish, the ability to process complex parts without the need of secondary operations, and low cost for mass production. However, because of the complex deformation, and thermal and pressure histories that the polymer melt experiences during processing, residual stresses develop. These stresses act internally at room temperature and have the same effects on the material as externally applied stresses do, resulting in shrinkage and warpage of the product. In recent years, with the development and use of engineering plastics in an increasing number of applications, and with the tougher quality control policies in industries such as the automotive, the effects of residual stresses in product quality and performance have raised great interest. This review reports up-to-date advances in the field of residual stresses developments in polymers, with special attention given to injection molded products. Flow- and thermal-induced residual stresses are reported. Emphasis is given to the processing parameters that most influence residual stresses during injection molding as well as the effect of residual stresses not only on warpage but also on other material properties.

Residual stresses in injection molded products

Three-dimensional numerical and experimental investigations on polymer rheology in meso-scale injection molding

i PREFACE iii LIST OF ORIGINAL PUBLICATIONS iv AUTHOR’S CONTRIBUTION iv LIST OF SYMBOLS AND ABBREVIATIONS vi

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Rheological characterization of polymer melts in shear and extension : measurement reliability and data for practical processing

This paper suggests a fractal two-phase fluid model for the polymer melt filling process to deal effectively with the unsmooth front interface. An infinitesimal fluid element model in a fractal spa...

A fractal two-phase flow model for the fiber motion in a polymer filling process

A numerical approach is introduced to solve the viscoelastic flow problem of filling and post-filling in injection molding. The governing equations are in terms of compressible, non-isothermal fluid, and the constitutive equation is based on the Phan–Thien–Tanner model. By introducing some hypotheses according to the characteristics of injection molding, a quasi-Poisson type equation about pressure is derived with part integration. Besides, an analytical form of flow-induced stress is also generalized by using the undermined coefficient method. The conventional Galerkin approach is employed to solve the derived pressure equation, and the ‘upwind’ difference scheme is used to discrete the energy equation. Coupling is achieved between velocity and stress by super relax iteration method. The flow in the test mold is investigated by comparing the numerical results and photoelastic photos for polystyrene, showing flow-induced stresses are closely related to melt temperatures. The filling of a two-cavity box is also studied to investigate the viscoelastic effects on real injection molding.

Chunjie Zhang

Papers

Computing flow-induced stresses of injection molding based on the Phan–Thien–Tanner model